A wide variety of processes use cross flow reactors to provide for contact between a fluid and a solid. The solid usually comprises a catalytic material on which the fluid reacts to form a product. The processes cover a range of processes, including hydrocarbon conversion, gas treatment, and adsorption for separation.
Cross flow reactors are often radial flow reactors and are constructed such that the reactor has an annular structure and that there are annular distribution and collection devices. The devices for distribution and collection incorporate some type of screened surface. The screened surface is for holding catalyst beds in place and for aiding in the distribution of pressure over the surface of the reactor to facilitate radial flow through the reactor bed. The screen can be a mesh, either wire or other material, or a punched plate. For a moving bed, the screen or mesh provides a barrier to prevent the loss of solid catalyst particles while allowing fluid to flow through the bed. Solid catalyst particles are added at the top, and flow through the apparatus and removed at the bottom, while passing through a screened-in enclosure that permits the flow of fluid over the catalyst.
In radial bed reactors with substantially continuous catalyst circulation, the forces exerted on the catalyst by the gas flow must be considered to ensure uninhibited catalyst movement. The direction of the gas flow through the catalyst bed is generally perpendicular to the desired direction of catalyst movement in the active bed. Under the right conditions, excessive gas velocities may impact catalyst movement either by holding up solids flow or creating a void space. Both are undesired affects which will adversely impact the flow of catalyst.
Among the processes utilizing radial flow reactors, the dehydrogenation of hydrocarbons is an important commercial hydrocarbon conversion process because of the existing and growing demand for dehydrogenated hydrocarbons for the manufacture of various chemical products such as detergents, high octane gasolines, oxygenated gasoline blending components, pharmaceutical products, plastics, synthetic rubbers, and other products which are well known to those skilled in the art.
The production of olefins by means of catalytic dehydrogenation of paraffinic hydrocarbons is well known to those skilled in the art of hydrocarbon conversion processing. Many patents discuss the dehydrogenation of hydrocarbons in general, such as for example, U.S. Pat. No. 4,430,517 (Imai et al), which discusses a dehydrogenation process and catalyst for use therein.
FIG. 1 illustrates one type of radial bed reactor 10. Catalyst enters the top of surge hopper 15 and flows into annular bed 20 as catalyst is withdrawn from the bottom of bed 20 via catalyst transfer lines 25. Inner perforated cylinder 30 and outer perforated cylinder 35 retain catalyst in annular catalyst bed 20 and at least partially define boundaries of distribution space 40 and collection space 45. As illustrated, there is an optional central distributor plug 50 which occupies the central portion of reactor 10 surrounded by inner perforated cylinder 30 and serves to distribute incoming reactants while minimizing the volume of distribution space 40. Reactants enter distribution space 40 through closed conduit section 55 that extends to the bottom of inner perforated cylinder 30. Collection space 45 on the outside of outer perforated cylinder 35 serves as a collection zone that supplies the reactor effluent for discharge through nozzle 60. The base plate 65 at the bottom of the catalyst bed 20 is flat.
However, under certain conditions this arrangement may allow the catalyst to become stagnant at the bottom the bed.
Therefore, a reactor with improved flow characteristics would be desirable.